The present disclosure relates to centrifugal compressors used for compressing a fluid such as air, and more particularly relates to centrifugal compressors and methods in which surge of the compressor is controlled by bleeding off a portion of the at least partially compressed fluid and recirculating the portion to the inlet of the compressor.
Centrifugal compressors are used in a variety of applications for compressing fluids, and are particularly suitable for applications in which a relatively low overall pressure ratio is needed. A single-stage centrifugal compressor can achieve peak pressure ratios approaching about 4.0 and is much more compact in size than an axial flow compressor of equivalent pressure ratio. Accordingly, centrifugal compressors are commonly used in turbochargers for boosting the performance of gasoline and diesel engines for vehicles.
In turbocharger applications, it is important for the compressor to have a wide operating envelope, as measured between the “choke line” at which the mass flow rate through the compressor reaches a maximum possible value because of sonic flow conditions in the compressor blade passages, and the “surge line” at which the compressor begins to surge with reduction in flow at constant pressure ratio or increase in pressure ratio at constant flow. Compressor surge is a compression system instability associated with flow oscillations through the whole compressor system. It is usually initiated by aerodynamic stall or flow separation in one or more of the compressor components as a result of exceeding the limiting flow incidence angle to the compressor blades or exceeding the limiting flow passage loading.
Surge causes a significant loss in performance and thus is highly undesirable. In some cases, compressor surge can also result in damage to the engine or its intake pipe system.
Thus, there exists a need for an improved apparatus and method for providing compressed fluid, such as in a turbocharger, while reducing the occurrence of compressor surge. In some cases, the prevention of compressor surge can expand the useful operating range of the compressor.